Apparatus for locking and related releasing of closure devices of doors of machines, more particularly for washing machines

ABSTRACT

An apparatus for locking and belated releasing of closure devices of doors of machines, more particularly for washing machines, wherein a latch cooperating with the door closure hook is held in locking position during the operation of the machine by a pin which releases it with a certain time delay after switching off the machine motors, so that the door can be opened only when the members of the machine subject to inertial rotation are at a complete standstill. This time delay is obtained through a fluid pump, thermostat or other suitable device, while the latch is locked during the operation by means of an electromagnet or circuit resistance coiled on the thermostat connected to the machine starting pushbutton.

United States Patent Rocchitelli July 1, 1975 APPARATUS FOR LOCKlNG AND3,451,233 6/1969 Shopsky 68/12 R RELATED RELEASING 0F CLOSURE 3,458,6757/]969 Del Gaudio... ZOO/61.64 3,617,957 11/1971 Brighenti ZOO/61.64

DEVICES OF DOORS 0F MACHINES 3.674.952 7/1972 Ellenberger ZOO/61.64

MORE PARTICULARLY FOR WASHING MACHINES Inventor: Onofrio Rocchitelli,20, Via

Stoppani, Rho, Italy Filed: Nov. 24, 1972 Appl. N0.: 309,415

Primary ExaminerDavid Smith, Jr. Attorney, Agent, or FirmRoland T. Bryan{5 7} ABSTRACT An apparatus for locking and belated releasing of closuredevices of doors of machines, more particularly for washing machines,wherein a latch cooperating with the door closure hook is held inlocking position during the operation of the machine by a pin whichreleases it with a certain time delay after switching off the machinemotors, so that the door can be opened only when the members of themachine subject to inertial rotation are at a complete standstill. Thistime delay is obtained through a fluid pump, thermostat or othersuitable device, while the latch is locked during the operation by meansof an electromagnet or circuit resistance coiled on the thermostatconnected to the machine starting pushbutton.

8 Claims, 13 Drawing Figures FIGS APPARATUS FOR LOCKING AND RELATEDRELEASING OF CLOSURE DEVICES OF DOORS OF MACHINES, MORE PARTICULARLY FORWASHING MACHINES BACKGROUND OF THE INVENTION Field of the Invention Thepresent invention relates to an apparatus for locking and belatedreleasing of closure devices of doors of machines having internal partsrotating at high speed, more particularly for washing machines.

2. Description of Prior Art It is known the necessity of providing onthe doors of machines having internal parts rotating at high speed, suchas washing machines apparatus adapted to lock the closure device of themachine door at start of the machine, and to release it with a certaindelay in respect to the current interruption. so as to hinder theopening of the door when some members of the machine may still besubject to an inertial rotation. such as the centrifuge basket. Someapparatus of this kind are already known. in which the releasing delayis obtained through the cooling action of a bimetallic device.

OBJECTS OF THE INVENTION Primary object of the present invention is toprovide a door locking device, giving a wide safety guarantee, as itlocks the door before starting the machine, keeping the locking actionthroughout the entire operation of the machine and after interruption ofthe current until any rotating member is completely standstill.

Furthermore, the door locking device according to the present inventionhas also the function of switch series connected to the door. so as toavoid closure of the machine actuating circuits if the door is notperfectly closed. and this device is placed in a position which cannotbe reached by the user so that it is absolutely impossible to actuatethe machine. even voluntarily. with the door open.

SUMMARY OF THE INVENTION The apparatus of the present inventionsubstantially consists of a sliding latch cooperating with the hook ofthe door closure lock, said latch being associated with a pin adapted tolock the latch when some conditions are occurring. said pin beingactuated, in a first embodiment of the invention. by an electromagnetconnected to the machine actuating controls and its opening beingdelayed by a fluid pump.

According to another embodiment of the invention the delay is obtainedby a device made according to the known wax thermostats (widely used inthe automative industry), suitably modified and improved, wherein a pinheld in a container partially filled with a particular wax. is expelledby the expansion of wax caused by heating of said container and iswithdrawn under an external thrust during the cooling stage of saidcontainer.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be betterunderstood with reference to the illustrative and non limiting embodiments which will be described in detail hereinafter with the aid of theaccompanying drawings, in which:

FIG. I is a sectional view of the detail of the positions of the latchand door closure hook with the door open, common to all the embodimentsof the invention;

FIG. 2 is a sectional view of the detail of the apparatus latch when thedoor is closed and the relative position of said latch and of the doorclosure lock. common to all the embodiments of the invention;

FIG. 3 is a partly sectioned view of the apparatus with electromagnetand delaying air pump in the rest stage with open door;

FIG. 4 is a view of the apparatus with electromagnet and delaying airpump in the working stage, locking the closed door;

FIG. 5 is a plan and sectional view on enlarged scale of the detail ofthe piston of the delaying pump;

FIG. 6 is a view of the apparatus with electromagnet and delaying liquidpump in the rest stage with open door;

FIG. 7 is a view of the apparatus with electromagnet and delaying liquidpump in the working stage. locking the closed door;

FIG. 8 is a view of the apparatus with wax thermostat in the rest stagewith open door;

FIG. 9 is a view of the apparatus with wax thermostat in the workingstage with lock of the closed door;

FIG. 10 is a View of an apparatus similar to FIG. 8, with theapplication of the control device for washing machines with electronicprogram;

FIG. 11 is a view of an apparatus similar to FIG. 9. with theapplication of the control device for washing machines with electronicprogram;

FIG. I2 is an enlarged detail of FIG. I0; and

FIG. I3 is an enlarged detail of FIG. II.

In all the figures the parts which are not modified will be indicatedwith the same reference numerals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference toFIGS. 1-5 the door locking device according to a first embodiment of theinvention consists of a box I for containing all the members oftheapparatus. said box containing more particularly at latch 2 engaging andlocking the head ofa hook 3 of the machine door lock.

This latch 2 is constantly held urged downwards by the spring 4 and atits top there is a hole 5 for a locking pin 6. Latch 2 is held in axialposition of hole 5 with pin 6 through the pawl 7.

The locking pin 6 is constantly held in opening position by the actionof spring 8 and with its extension 9 passes through the fixed magneticcore I0 and at its end is provided with a vibration dampening gasket IIthrough which it leans the movable core I2.

Electromagnet is formed by an external core I3 en velopping itcompletely, so as to keep enclosed the electromagnetic flux, a coil I4,the movable core l2 and the fixed core 10. The movable core 12 is forwardly extended with a stem 15 ending with the piston I6 which can slidein a chamber I7. Said chamber is in communication with the atmosphere atthe stem through the gap existing around the movable core I2.

Piston I6 is formed by a frustum-conical body of plastic material havingthe cross section shown in FIG. 5 and bearing at its upper flat portiona set of very little holes 27 ofa number and sizes varying according tothe desired time delay.

Piston 16 in its closure position (from left to right in FIG. 3) allowspassage of air through its outer edges 16, which on the contrary have asealing effect when the piston is moving in the contrary direction. sothat the fluid is compelled to pass through said holes 27 delaying thereturn stroke.

In the apparatus there is also a microswitch unit comprising a bladewith contact 18 actuated by the pushbutton 19 and born by a Zlike arm 20which can be rotated around pin 2i. whose opposite end 22 is arranged atthe hole 23 for the introduction of hook 3 of the door, and having itsterminal 24 connected to one of the poles of the current supply line.The other end of the current supply line reaches the terminal 25.

The energization circuit of the coil is ending at the terminals 25 and26 so that it is energized only when the door lock hook acting on theend 22 of arm 20 lets current to pass to the coil.

The operation of the apparatus is the following: upon closure of thedoor of the washing machine, its hook 3 is inserted on one side into therecess 23 so as to act with the lower part on the end 22 of arm 20 so asto lower it and to keep it in said position (see FIGS. l2) and with theupper part on the latch 2 so as to become associated thereto (see alsoFIGS. 1-2).

Following this action arm 20 is moving downwards, so that lever 20rotating around the pin 21 causes the pushhutton 19 to act on blade 18of the microswitch so as to close the circuit of energization of thecoil of the electromagnet.

In consideration of the energization of the coil, the fixed core ismagnetized, attracting the movable core 12 which in turn urges the pin 6to be inserted in the hole 5 of the latch 2 and the air contained in theupper part of the chamber passes in the lower part of chamber 17. Thewhole remains in this conditions up to the completion of the workingcycle of the machine.

The vibration dampening gasket 11 has the function to avoid that thevibrations of the movable core 12 be cause of the current circulating inthe coil. are passing to the latch 2.

At the end of the working cycle. the current at the terminals 2525 isinterupted by the machine control unit so that the coil is disenergizedand under the push of spring 8 the pin 6 may be withdrawn and comesoutfrom the hole 4 releasing the latch 2, allowing lifting andextraction of the hook of the machine door.

However, this does not happen immediately. but after a certain period oftime according to calibration of the apparatus, that is according to thegreater or lower resistance to the passage of air from one side to theother of the chamber 17, resistance which is made by the holes 27 of thepiston 16.

Opening of the machine door may therefore take place only when the pin 6is completely disengaged from hole 5, that is after those predeterminedl045 seconds spent by the piston 16 under the action of the spring, toreturn from position of FIG. 4 to that shown in FIG. 3.

in the case that for the operation of the delaying pump it is desired touse a liquid such as oil, instead of air, the apparatus is modified asshown in FIGS. 6 and 7. In other words the chamber 17 instead of beingin communication with external air through the outer walls of themovable core 12 at its upper part, is closed by a complementary chamber28 which acts a seal on the shaft of the piston, and such a chamber 28is filled with a liquid which passes from one side to the other of thepiston 16 according to its movements.

To the terminal 26 where one of the poles of the coil arrives, isconnected also the wire for returning tension to all other movements ofthe machine, so that the same microswitch, in addition to be used ascontrol for the operation of the locking circuit, has also the func tionof interrupting the series of control circuits of the machine, becausethe machine cannot start operation with the door open, as it can not beactuated if the door book did not push downwards the lever 22. Moreoverthis control is arranged in a not accessible position and can beactuated only by the book of the machine door.

A second embodiment of the present invention is shown in FIGS. 8 and 9wherein all the other members of the apparatus are unaltered, but themoving and timing element consists of an apparatus made along the knownprinciples of a wax thermostat. substantially comprising an internallyhollow metal body which is partially filled with a particular wax havinga high thermal expansion coefficient, eventually mixed with additives(copper, aluminum powder etc.) and on which a pin or piston is insertedand held in contact with the wax by means of an external thrust, saidpiston being expelled when the ambient in which said hollow body of thethermostat is inserted, is brought to a higher temperature because ofthe expansion of the wax, and always under the thrust of the externalelement, is withdrawn when the ambient in which the hollow body of thethermostat is inserted is cooled and the wax returns to its originalvolume.

Such a type of thermostat is widely used in the automotive industry andis generally applied on the engine cooling circuit, to control variousmembers connected to said circuit. Such a thermostat has a reliable andlasting operation allowing tens of thousands of operations.

it is however to be understood that the invention does not only compriseonly the application of a known wax thermostat device, as theconventional wax thermostats for the automotive industry cannot beapplied in this case because they are too slow in their extractionmovement, they fuse and therefore the phenomenon of the wax expansiontakes place at a temperature of about 8()90 and they cool down also veryslowly, while for the present application to washing machines it isrequired an almost immediate extraction and a withdrawal within a periodof approximately 15 to seconds.

Some measures were tested for speeding up the operations moreparticularly of the expansion phase, by making thermostat bodies withvery thin outer walls in order to feel at once the effect of a heatsource placed outside them, but the maximum effort was above all tochoose with advantage for the duration, substances having in addition toa high coefficient of thermal expansion and a high velocity ofexpansion, a lower melting point, that is between 40 and C.

It has been found that this object is well met by some paraffins withlow melting point, as substitution for the already known waxes, and moreparticularly a phisical mixture comprising of butil behenate:

CH3 (CH2) 20 CO O CH2 zlz CH1! and 45% of stearyl adipate:

co o H a c 2 (C CH This mixture has a melting point of 496C, allows themanufacture of thermostat bodies with walls having a thickness notgreater than l5/100 of millimeter, has a considerable velocity ofexpansion so that it is possible to obtain thermostats capable ofexpelling the piston on a time of 1-3 seconds and to withdraw in -45seconds, varying the wall thickness, density of the mixture and heatsource.

In order to make possible the variation of the pin withdrawal time andtherefore the door releasing time, but keeping unaltered in a certainrange the velocity of return of the wax thermostat itself, so that withone thermostat having always the same dimentions and characteristics itis possible to obtain different locking speeds with a simplemodification ofa little detail of the apparatus in order to meet thedifferent requirements of the variuos manufacturers, to the pin orpiston of the wax thermostat and more particularly between it and thehole 5 of the latch 2 it has been inserted a clutch connection formed bya cylinder ending with a pin, the latter being associated to the hole 5of Latch 2.

With reference now to FIGS. 1, 2, 8 and 9, the door locking deviceaccording to this embodiment of the present invention comprises, likethe preceding one, a box 1 for enclosing all the members of theapparatus. which more particularly contains a latch 2 which engages andlocks the head of the hook 3 of the machine door lock.

This latch 2 is held constantly urged downwards by a spring 4 and at itstop has a hole 5 for a locking pin of predetermined length, which is theextreme extension of a cylinder 29 provided with an internal cylindricalcavity 30 wherein it slides under friction exerted by a rubber ring 31and a rod 32.

In view of this coupling. when the cylinder 29 is free to move in eitherdirection, it is drawn by the eventual movement of the rod 32. If on thecontrary the cylinder 29 reached the stop 33 and 34 or for eventualinciden tal obstacles along its path, for instance lack of axialalignment of hole 5 with the extension 35 of the cylinder 29. it has tostop, the rod 32 slides inside the cavity 30, of the cylinder 29.

The latch 2 is held in a position of axial alignment of the hole 5 withthe extension 35 by means of the pawl 7. The locking pin 35 isconstantly held in the opening position by the spring 36 acting on therod 32.

The rod 32 is connected to the cylindrical body 37 which in turn isconnected to the piston 38 which through the interposition of a pad ofelastic material 39 (rubber, neoprene, etc.) partially fills the cavityof a cylinder 40 being the body ofa wax thermostat, the remainingportion of which is filled by a particular wax.

The cylinder 40 is sorrounded by an electric resis tance 41 having oneend connected to the terminal 25 and the other to the contact terminal42 and through the contact 43, spring 36 and contact 44 to the otherterminal 26.

In the apparatus there is a microswitch unit, like in the precedingembodiments, formed by a blade with contact 18 actuated by thepush-button 19 born by a Z like arm 20 capable of rotating around thepin 21 and the other end 22 reaching the hole 23 of introduction of thehook 3 of the machine door. and having the terminal 24 connected to oneof the wires of the current supply line.

The second wire coming from the current supply line reaches the terminal25.

The resistance circuit, as above said, ends at the ter' minals 25 and 26so that it is fed only when the machine door closure hook acting on theextreme part 22 of the lever 20 supplies tension to the resistance 41.

The operation ofthe apparatus is the following; Upon closure of the doorof the washing machine. its extreme hook 3 is inserted from one side inthe recess 23, acting with its lower part on the end 22 of the lever 20so as to lower and keep it in such a position (see details in FIGS. 1and 2) and with the upper part on the latch 2 so as to become associatedthereto (see also FIGS. 1 and 2) Following this action the arm 20 ismoved downwardly, so that lever 20 rotating around the pin 21 causes thepushbutton 19 to act on the blade 18 of the microswitch, closing thecircuit and supplying tension to the resistance 41.

In consideration of the passage of current through the resistance 4],this is being heated and because of the production of heat the waxcontained in the cylinder 40 is expanded pushing forward the gasket 39and the piston 38 and consequently the rod 32 which in turn pushesforward the cylinder 20 so that the pin 35 made at its end is insertedinto the hole 5 and locks the latch 2 (see FIG. 9), until said cylinder29 stops because its fore surface reaches the wall 34 of the body 1.

In the meantime rod 32 may go on in its forward movement, sliding in theinner cavity 30 of the cylinder 29. In this position the contacts 42 and43 are being separated so as to break the current feeding the resistance41 which as a consequence cools down (see FIG. 9).

Subsequently as a consequence of the thrust of the spring 36 the pin 32slightly goes back at that moment the two contacts 42 and 43 are matchedand supply again tension to the resistance which is heated and becauseof the expansion of wax the pin 32 is again pushed forwards. Thisphenomenon of very little alternate continuous movements of the pin 32of the order of hundreths lasts for the whole period of operation of themachine.

When the machine stops at the end of the working cycle, the current tothe terminals 25 and 26 is interrupted, resistance 41 and therefore waxcontained in the cylinder 40 are cooled and rod 32 because of the effectof the thrust of spring 36 against the body 37 re turns to its place,drawing the cylinder 29 and releasing the latch 2.

During its return rod 32 drags cylinder 29 until the latter stopsagainst shoulder 33 of the body 1, while the rod 32 goes on withdrawingcoming out from the cavity 30.

Thus, increasing or decreasing the lenght of the pin 35, it is possibleto increase or decrease the time of releasing the latch 2 and thereforeof opening the door, using the same thermostat 12.

In order to make easier the cooling of the device in this stage,cylinder 40 may be provided at both ends with a plurality of coolingpins 45, whose dimensions are depending from the return speed of thepiston 38.

The elastic pad 39 interposed between the wax and the piston 38 has thefunction of acting as a sealing gasket for avoiding emission of wax inthe event of overheating and for warranting this function it is slightlypacked of the action exerted on it by spring 36 on piston 38.

When a door locking apparatus must be applied on machines havingelectronic programmers, the apparatus according to the present inventionis provided with a further microswitch shown in FIGS. 10 to 13.

In fact it is known that if the electronic programmer is subjected for atoo long time to the main current, more particularly during the take-offperiod of the mo tors, the electronic circuit deteriorates.

In such a case of the movable member actuated by the device controllingthe latch locking pin (in the instance of the embodiment of FIGS. l-l3the movable contact 43) is mounted the insulating pin 50 ofa microswitchcomprising a base fixed on the box 1 containing the various elements ofthe device, two fixed contacts 52 and 53 series connected on the circuitof energization of the electronic programmer and the movable contact 54fixedly joined to the insulating pin 50 electrically connected with thecontact 53 through the led 55.

Therefore, when the movable contact 54 is in contact with the contact42, the circuit of the electronic programmer is closed and the currentof the electric circuit of the machine passes through it. but when thisis detached. the current of the electronic programmer is interrupted.

The operation of the device is the following:

As a consequence of the closure of the door of the ma chine its extremehook 3 is inserted in the cavity 23 acting with its lower part on theend 22 of the lever in order to lower it and with its upper part on thelatch 2 in order to become associated to it.

Following this action the arm is moved downwardly, so that the lever 20rotating around the pin 21 causes the pushbutton 19 to act on tha blade18 of the microswitch. closing the circuit and supplying tension to theresistance 41.

In view of the passage of current through the resistance 41. the latteris being heated and because of the heat produced the wax contained inthe cylinder is expanded. pushing forward the gasket 39 and the piston38 and consequently the rod 32 which pushes forward the cylinder 29 sothat the pin 35 made at its opposite end is inserted in the hole 5 andlocks the latch 2 (see FIG. 2), until said cylinder 29 stops because itsfront surface reaches the wall 34 of the body l.

in the meantime the rod 32 goes on moving forward, sliding in the innercavity 34 of the cylinder 29. In this position the contacts 42 and 43are being separated interrupting the current feeding the resistance 4!which consequently is cooled down. The contact 43 in the meantime pushedforward the piece 50 bearing the movable contact 54 (see FIGS. 11 and13) which is detached from the fixed contact 52 and the current to theelectronic programmer is interrupted.

As a consequence. under the thrust of the spring 36 the pin 32 isslightly withdrawn but at that moment the two contacts 42 and 43 arejoined supplying again ten sion to the resistance which is being heatedand under the effect of the expansion of the wax it pushes again forwardthe pin 32.

This phenomenon of very little continuous alternate movements of the pin32 of the order of hundreths lasts for the whole operation time of themachine. During all this time the contacts 52 and 53 are howeverconstantly detached.

When the machine stops at the end of its working cycle, the current tothe terminals 25 and 26 is interrupted, the resistance 41 and thereforethe wax contained in the cylinder 40 is cooled and the rod 32 because ofthe thrust ofthe spring 36 against the body 37 returns to its placedrawing the cylinder 29 and releasing the latch 2. The contact 54 isagain associated to the contact 52 closing the circuit to the electronicprogrammer and the machine is ready for another starting.

l claim:

I. For use in controlling the locking and releasing of latching deviceson access closures in machines such as washing machines and the like,internal members of which machines preferably cease movement prior tothe time when such closures may be opened for internal access thereto.which latching devices include a moveable latch device for cooperativeinterengagement with an associated hook member, which latch is to belocked in closed position during operation of the machine by a lockingpin and is to be unlocked by actuation of said locking pin at the end ofthe machine operation with a pre-determined time delay, apparatuscomprising a locking pin actuated by a piston moveable in a chamber,means for selectively heating said chamber according to the operativecondition of the machine, and a heat expansible. low melting point waxcontained in said chamber, expansion of which wax will cause actuationof said locking pin to effect locking of said latch in closed positionand contraction of which wax will cause actuation of said pin to effectunlocking of said latch.

2. A device as described in claim I wherein said heating means comprisesan electrical resistance heater which surrounds said chamber.

3. An apparatus as claimed in claim 2 wherein a pole of the electricalresistance heater is divided into two contacts, one of which is fixedand the other is movable with the piston so that the two maintaincontact and complete an electrical circuit except when the piston isactuated by the wax thermostat to position the locking pin in lockedposition whereby the locking pin is maintained in a locked positionwithout continuous applica tion of electrical energy to the electricalresistance heater and without wax over-heating and excessive pressuregeneration within the chamber.

4. An apparatus as claimed in claim 2, wherein a pad of elastic materialis interposed between the wax and the piston to act as a gasket for thewax in the melting stages.

5. An apparatus as claimed in claim 2, wherein the expansible waxcomprises a mixture of waxes having a melting point below about C.

6. An apparatus as claimed in claim 5, wherein the wax mixture comprisesa physical mixture of 45 percent butyl behenate and 55 percent stearyladipate.

7. An apparatus as claimed in claim 2 wherein the piston is operativelyconnected to the locking pin by means of a piston rod connected to thepiston and slidably positioned within a hollow cylinder formed by oneend of the locking pin whereby inadvertent energization of the waxthermostat under conditions of misalignment of the locking pin and latchdo not result in unsafe operation.

8. A device as described in claim 7 wherein the locking end ofthelocking pin is selectively replaceable with locking ends of variouslengths without modifying the piston rod or hollow cylinder, whereby thevelocity of the piston movement may remain the same while the waxthermostat is usable for obtaining different unlocking times.

1. For use in controlling the locking and releasing of latching deviceson access closures in machines such as washing machines and the like,internal members of which machines preferably cease movement prior tothe time when such closures may be opened for internal access thereto,which latching devices include a moveable latch device for cooperativeinterengagement with an associated hook member, which latch is to belocked in closed position during operation of the machine by a lockingpin and is to be unlocked by actuation of said locking pin at the end ofthe machine operation with a pre-determined time delay, apparatuscomprising a locking pin actuated by a piston moveable in a chamber,means for selectively heating said chamber according to the operativecondition of the machine, and a heat expansible, low melting point waxcontained in said chamber, expansion of which wax will cause actuationof said locking pin to effect locking of said latch in closed positionand contraction of which wax will cause actuation of said pin to effectunlocking of said latch.
 2. A device as described in claim 1 whereinsaid heating means comprises an electrical resistance heater whichsurrounds said chamber.
 3. An apparatus as claimed in claim 2 wherein apole of the electrical resistance heater is divided into two contacts,one of which is fixed and the other is movable with the piston so thatthe two maintain contact and complete an electrical circuit except whenthe piston is actuated by the wax thermostat to position the locking pinin locked position whereby the locking pin is maintained in a lockedposition without continuous application of electrical energy to theelectrical resistance heater and without wax over-heating and excessivepressure generation within the chamber.
 4. An apparatus as claimed inclaim 2, wherein a pad of elastic material is interposed between the waxand the piston to act as a gasket for the wax in the melting stages. 5.An apparatus as claimed in claim 2, wherein the expansible wax comprisesa mixture of waxes having a melting point below about 50*C.
 6. Anapparatus as claimed in claim 5, wherein the wax mixture comprises aphysical mixture of 45 percent butyl behenate and 55 percent stearyladipate.
 7. An apparatus as claimed in claim 2 wherein the piston isoperatively connected to the locking pin by means of a piston rodconnected to the piston and slidably positioned within a hollow cylinderformed by one end of the locking pin whereby inadvertent energization ofthe wax thermostat under conditions of misalignment of the locking pinand latch do not result in unsafe operation.
 8. A device as described inclaim 7 wherein the locking end of the locking pin is selectivelyreplaceable with locking ends of various lengths without modifying thepiston rod or hollow cylinder, whereby the velocity of the pistonmovement may remain the same while the wax thermostat is usable forobtaining different unlocking times.